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Doug, Australia Car Mechanic
Category: Australia Car
Satisfied Customers: 8618
Experience:  ASE Certified Factory trained technician
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Magna Es 2004 140k. Stalling v occasionally when setting off

Customer Question

Magna Es 2004 140k. Stalling v occasionally when setting off or picking up from low speed. Auto box of course. External diagnostics showed nothing. Ideas ;-)
Submitted: 1 year ago.
Category: Australia Car
Expert:  Doug replied 1 year ago.


I would be mostly interested in the idle control functions as problems here can cause this type of behavior and not throw any codes, so everything looks OK on a diagnostic scan.

With the engine warmed up and idling stable, turn the AC on/off and watch the idle speed behavior, and do the same with loading up the power steering. What we want to see if each time the steering is loaded up the idle goes up about 200RPM, and each time the AC is turned on the idle goes up 100-200RPM, the load from the compressor kicks in and brings it back down to normal.
What we don't want to see is the idle going down when either load is added. If you do see that, then the idle air control valve is likely at fault, as it is not idling-up when it is supposed to; while this could be the valve, the ecu or the wiring, it is generally only the valve at fault here.
If you see normal idle-up behavior, then I would want to remove the intake hose and thoroughly clean the inside of the throttle body with a brake cleaner saturated rag (never spraying into the throttle). The entire inside around the sealing area of the throttle plate should be absolutely spotless; the very fine black/brown soot that builds up in there will cause random stalling when it is too much for the idle valve to overcome... and it does not take a lot, we are dealing with thousandths of an inch increments there.

If the idle up is working and the cleaning of the throttle is no help either, things will get much more involved very quickly; the last basic test that would need to be done would be to check the fuel conditions... pressure and quality. The easiest way for a shop to do this is to supply an auxiliary fuel supply (pressurized can) and see if the issue goes away, and of course if it does then investigation into the fuel pump/regulator/fuel quality would be in order. If there is no change whatsoever, then it will be time for in-depth analysis... meaning bringing a drive recorder in the car and logging all sensor inputs (engine and transmission too just in case there is something odd going on in there affecting the condition) to see what is occurring from the computers perspective when the problem occurs. This will require a trip to the Mitsubishi dealer to do this though, as the Holden scan tools will not communicate at a manufacturer level with the Mitsubishi for logging, only generic OBD access which is not sufficient for this level of diagnosis.